W. Newlon Tauxe

Tc-99m hexamethylpropylene amine oxime scintigraphy in the diagnosis of Brain death and its implications for the harvesting of organs used for transplantation

PURPOSE Diagnosing brain death is important in managing the comatose patient for whom the continuation of life support is being questioned and when organ harvesting is being considered. The virtual immediate localization of Tc-99m HMPAO to cerebral and cerebellar tissue provides an index of blood perfusion, and its absence denotes brain death. Other methods for assessing brain death include cerebral angiography, MRI, CT imaging after inhalation of stable xenon, electroencephalography, and clinical examination. The contrast material used for angiography may damage harvested organs, and the other studies have significant errors. MRI, CT imaging, and angiography are unsuitable for bedside use. METHODS Twenty-three patients, who presented with head trauma, prolonged anoxia or intrinsic brain disease (e.g., glioblastoma multiforme) and who were brain-dead by clinical examination criteria, were referred to the nuclear medicine division for verification of brain death. For adults, approximately 25 mCi Tc-99m hexamethylpropylene amineoxime (HMPAO) was administered intravenously. All patients but one were imaged using a mobile scintillation camera at the bedside. RESULTS We demonstrated (1) both cerebral and cerebellar perfusion, (2) neither cerebral nor cerebellar perfusion, (3) cerebral without cerebellar perfusion, and (4) cerebellar without cerebral perfusion. Patients without cerebral perfusion were diagnosed as brain-dead. The significance of a viable cerebellum in the absence of cerebral viability was not fully appreciated, although organs were harvested from such patients. We determined how well the clinical examination criteria held up in the diagnosis of brain death against the new gold standard of Tc-99m HMPAO scintigraphy: Clinical examination criteria correctly predicted brain death only 83% of the time compared with HMPAO scintigraphy. CONCLUSIONS Brain death assessment by Tc-99m HM-PAO scintigraphy has proved to be a reliable, safe, and cost-effective bedside method and may have practical application in the assessment of brain death in potential cadaveric donors.

Detection of complications after liver transplantation by technetium-99m mebrofenin hepatobiliary scintigraphy

Fifty-five hepatobiliary scintigraphic studies using99mTc-Mebrofenin were performed in 52 orthotopic liver transplant patients to evaluate suspected biliary complications, namely biliary extravasation and extrahepatic obstruction. Final diagnosis was made by analysis of the clinical course and other procedures.Three out of three studies of biliary leak and four out of five studies of biliary obstruction were detected. There were no false positives in either complication. The sensitivity, specificity and accuracy were 100, 100, 100% for ectravasation and 80, 100, 98% for obstruction, respectively.Hepatobiliary scintigraphy appears to be an accurate means of detecting biliary leak and obstruction associated with the transplanted liver.

Comparison of measurement of effective renal plasma flow by single plasma sample and plasma disappearance slope/volume methods

Numerous simplified methods for the estimation of ERPF have been described, including the so-called slope/intercept (SI) methods, based on the analysis of the slope of certain segments of the131I-OIH plasma disappearance curve and its y-axis intercept, and the single sample (SS) clearance method, based on theoretical volumes of OIH distribution at some fixed time after injection. Using ERPFs estimated from compartment analysis of the entire 60-min plasma disappearance curve, we have compared the errors of data calculated from use of eight SI methods made at various times along the disappearance curve with that from the optimum SS curve. The errors obtained from the SS method were approximately 50% less than those obtained from the SI methods. The errors of the SI methods are greater at both ends of the 60-min plasma curve than when samples are drawn near the mid-time. The SS method appears to be the method of choice for the estimation of ERPF using single injection techniques.

Evaluation of portal-systemic shunting in rats from mesenteric and splenic beds

In rats with partial portal vein ligation, 95±0.9% of the splenic blood flow is shunted from the portal to the systemic circulation when an intrasplenic injection of microspheres is used to determine the degree of shunting. Despite this magnitude of portal-systemic shunting, several biochemical and endocrine consequences of portal-systemic shunting occur at levels below what is expected for the degree of shunting found. In an effort to resolve these discordant findings, shunting from both the splenic and the mesenteric bed was studied in anesthetized portal hypertensive rats with various degrees and/or duration of portal vein stenosis. The shunting from the mesenteric bed averaged 66.7±29.9% (range 5.1–99.1%) and was influenced both by the degree and duration of portal vein stenosis. In contrast, shunting from the splenic bed averaged 97.3±4.0% (range 79–99.9%) and demonstrated no variation between groups determined by the degree of portal vein stenosis. The shunting from the splenic bed was consistently greater than that found from the mesenteric bed. Mesenteric but not splenic shunting correlated with serum bile acid levels. Mesenteric shunting was related inversely to the weight-adjusted liver mass and to serum testosterone levels. Based upon these data obtained in portal hypertensive rats, it is concluded that splenic injections of microspheres overestimate portal-systemic shunting. In contrast, mesenteric injections of microspheres yield values for shunting that correlate well with independently determined biochemical and endocrine consequences of shunting. These observations support the validity of the mesenteric shunting measurements obtained.

An evaluation of the accelerated expectation maximization algorithms for single-photon emission tomography image reconstruction.

We previously reported that brain single-photon emission tomography (SPET) images could be improved by using an attenuation coefficient map constructed with transmission data and the iterative expectation maximization (EM) algorithm. However, the conventional EM algorithm (CEM) typically requires 30–80 iterations to provide acceptable results, limiting its clinical applicability. Several methods have been proposed to accelerate the EM algorithm. The purpose of this study was to search for a practical method for accelerating the EM algorithm. The methods investigated here include the accelerated EM algorithm (ACEM) using additive correction, ACEM using multiplicative correction, and Tanakas filtered iterative reconstruction method (FIR). These methods were assessed by simulated SPET studies of a phantom incorporating nonuniform attenuation and by reference to clinical brain SPET data. In the simulation studies, the above methods were evaluated by using three parameters (root mean square error, log likelihood value, and contrast recovery coefficient); the results showed that FIR had an advantage over other methods in terms of all parameters. The results obtained using the clinical data demonstrated that FIR could reconstruct acceptable images in only five iterations. These results show that FIR offers significant advantages over CEM or other ACEMs, indicating that FIR can make the EM algorithm practical for clinical use in SPET.

Comparison of measurement of glomerular filtration rate by single sample, plasma disappearance slope/intercept and other methods

Various in vitro methods employing radioactive indicators have been presented for the determination of glomerular filtration rate (GFR) including slope/intercept (S/I) and single sample (SS) methods. The S/I technique utilizes the analysis of the slope of a certain segment of the plasma disappearance curve of a suitable radioactive indicator and its intercept on the y axis. The SS method is based on the theoretical volumes of distribution derived from a single plasma concentration at some specific time after intravenous injection of the indicator. Using GFRs estimated from the compartmental analysis of the entire plasma disappearance curve as a reference standard, we have compared the errors of GFR estimation calculated from 12 S/I methods, 3 SS methods and 2 techniques in which original formulae were derived. The errors of the SS method of Tauxe et al. gave the lowest standard error of estimate (Sy·x) of all the methods. The S/I methods gave lowest errors when sampling times were taken between 60 min and 240 min. Almost all the errors observed here were significantly less than those observed using scintillation camera techniques. The SS method seems to be the method of choice for estimation of GFR by single injection techniques. The use of the scintillation camera in conjuction with the SS technique would provide a useful right to left ratio so that individual kidney GFR could be calculated.

Effect of isolated portal hypertension on kupffer cell function

The increased incidence of infection in cirrhotics may in part be attributable to dysfunction of the reticuloendothelial system (RES) in removing pathogens from the circulation. The portosystemic shunting (PSS) that results from portal hypertension in cirrhotics may compromise RES function by allowing enteric pathogens to be shunted away from the Kupffer cells. A well-characterized model of portal hypertension induced by partial portal vein ligation (PVL), in which there is no hepatic parenchymal cell damage, was used. Kupffer cell function is unaltered and the effect of PSS alone on overall RES function can be evaluated. In addition to the usual immunologically inert [99mTc]sulfur colloid, an actual pathogen was also evaluated. PVL and sham-ligated rats were given either [99mTc]sulfur colloid orE. coli via the ileocolic vein. The right femurs, lungs, livers and spleens of the animals receiving99mTc were excised and the radioactivity counted. The lungs, livers, and spleens of the animals receivingE. coli were liquefied and the bacteria were quantified. For both groups the ratios of99mTc orE. coli in the lung, spleen, and femur to liver were calculated. PVL rats had significantly more99mTc in the lung, spleen, and femur than the sham rats. There were also significantly moreE. coli in the lungs for PVL rats but no significant difference in the spleen counts. These results imply that even in the absence of Kupffer cell dysfunction, PSS alters reticuloendothelial system function by causing a greater distribution of pathogens to the periphery. This altered distribution may contribute to an increased susceptibility to infection in cirrhotics.

ECG-gated thallium-201 myocardial SPECT in patients with old myocardial infarction compared with ECG-gated blood pool SPECT

We evaluated one of the merits of ECG-gated thallium-201 single photon emission computed tomography (g-T1 SPECT), i.e., the ability to appreciate left ventricular (LV) wall motion. LV wall motion assessed by g-Tl SPECT and by ECG-gated Blood Pool SPECT (g-BP SPECT) was classified into three grades and compared segment by segment. T1-201 uptake by g-Tl SPECT was also classified into three grades and compared with those of wall motion in g-BP SPECT.Fifty patients with prior myocardial infarction were injected intravenously at rest with 111 to 185 MBq (3 to 5 mCi) of Tl-201. The left ventricular regions were divided into anterior, septal, inferior and lateral segments (50 patients × 4 segments=200 segments in total). The grades of wall motion and Tl-201 uptake detected by g-Tl SPECT correlated well with those of wall motion in g-BP SPECT (94.5% and 85%, respectively).With g-Tl SPECT it was possible to evaluate left ventricular wall motion, providing clear perfusion images.

Technetium-99m MDP scintigraphy of rhabdomyolysis induced by exertional heat stroke: A case report

A case of rhabdomyolysis induced by exertional heat stroke in a police officer recruit is reported. Technetium-99m methylene diphosphonate scintigraphy demonstrated marked uptake of the injured skeletal muscle. This bone-scanning agent provided an excellent means of localizing and evaluating the muscle injury of rhabdomyolysis. Nuclear medicine physicians should be aware of the special conditions and causes in which bone scan may demonstrate striking findings.

The use of quantitative scintigraphy in the measurement of portal-systemic shunting in rats

Portal-systemic shunting was studied in 54 portal hypertensive rats bothin vivo andin vitro using radioactive microspheres. The animals underwent partial portal vein ligation around needles of varying diameter to produce a wide range of shunting. Two to four weeks later, quantitative lung-liver scintigraphic and whole body images were obtainedin vivo following ileocolic vein injection with99mTc-MAA. After sacrifice, the lung and liver activities were determined by the gamma camera, a dose calibrator, and a well counter. Portal-systemic shunting ranged from 0.1–97.6%. When shunting was comparedin vivo andin vitro, an excellent correlation was found (r=0.99, p< 0.001). A subgroup of 24 animals had consecutive injections of99mTc-MAA and51Cr-labeled 15 μm microspheres, which, although different in size, yielded similar results (r=0.89, p< 0.001). We conclude that in small laboratory animals a wide range of shunting can be measured accuratelyin vivo by quantitative scintigraphy.